Production of ferromagnetic iron oxide



Aug. 18, 1959 w. c. SPEED ETA!- PRODUCTION OF FERROMAGNETIC IRON OXIDE Filed Aug. 3, 1955 M SHE m 2. mum m N 2. w w 5 m um mum w I w N0 B w 0 1 00 N 4 8 Ow Oh m u Sutheiin, Stamford, Conn., assignors to Audio Devices, Inc., New York, N.Y., a corporation of New York Application August 3, 1955, Serial No. 526,270 12 Claims. ((31.23-277) This invention relates to the production of ferromagnetic iron oxide and has for its object more particularl-y'theproduction of gamma ferric oxide which is highly ferromagnetic.

Most ferric oxides, natural or synthetic, are non-magnetic, but it is well known that such oxides, referred to commonly as alpha ferric oxides, can be transformed in a relatively simple manner intoferrosoferric oxide and then into gamma ferric oxide. The process consists of a reduction operation executed at elevated temperature, which transforms yellow (the monohydrate form) or red (the anhydride form) alpha ferric oxide, alpha Fe O into black ferrosoferric oxide, Fe Og, often called magnetite. The hot Fe O is carefully cooled and is then re-heated at a lower temperature and subjected to acarefully controlled oxidation operation which transforms the black Fe O into a yellowish brown gamma ferric oxide, gamma Fe O This two-step operation is performed on an industrial scale for a variety of purposes, e.g. magnetic ore separation, or preparation of magnetic core material for magnetic memory systems. The literature in journals and patents describes the reduction process to be executed by heating the non-magnetic alpha ferric oxide in the form of pellets or powders to a temperature of approximately 1000" F. in rich reducing atmospheres, such as hydrogen, carbon monoxide, city gas, dissociated ammonia, sulfur, etc. The use of hydrogen is very dangerous because of its explosive nature; and the other reducing agents are also dangerous because of their poisonous or noxious nature. The resultant product is cooled in an inert or reducing atmosphere to room temperature. generally is lengthy but is necessary because the black ferrosoferric oxide formed is strongly pyrophoric at elevated temperature, e.g. above 340 F., whereby its magnetic properties are seriously damaged. Therefore, the hot black ferrosoferric oxide must be carefully protected from any contact with air, and numerous precautions are suggested to prevent such contact, for instance, by cooling the oxide in the reduction furnace in the same reducing gas, quenching the hot material in water or other liquids, using Dry Ice for the cooling, using steam as a protecting atmosphere, etc. Even lengthy periods of cooling or quenching in water to prevent ignition of the magnetic black oxide are not adequate. The ferrosoferric oxide is very unstable immediately after reduction and, even though cooled, it often reoxidizes so rapidly in the presence of air as to reconvert the black oxide to its former alpha ferric oxide form. All of these precautions increase the costs of the operation without giving absolute guaranty for safe operation. 7

. The second step of oxidizing the back ferrosoferric oxide to yellowish-brown gamma ferric oxide is performed by.re-heating it cautiously in an oxygen containing atmosphere. Due to the pyrophoric properties of the ferrosoferric oxide this operation is also diflicult to control. If the temperature is too low, the transformation doe's not take place. If it is higher than necessary, the exothermic PQ t dSW Pate This latter step which is deleterious to the material.

nature of the process leads to a spontaneous overheating Therefore another set of precautions must be taken, either to work at 'as low a temperature as possible and take care of dissipating the exothermic heat effectively or to permit atany time only a limited amount of oxygen to get in touch with the heated ferrosoferric oxide to prevent rapid (exothermic) oxidation. 7

As a result of our investigations we have discovered that disadvantages of the kind enumerated can be overcome for the most part. Thus, we have found that the two-separate-steps operation can be modified into a continuous process conducted in a closed system. The equipment, which will be described in more detail below, permits the continuous feeding of raw material, reducing it in a hot zone, passing it without interruption into a somewhat cooler zone in which a counter stream of air is introduced: this immediately transforms the black Fe O into the finished gamma Fe O which is removed continuously. A number of advantages are achieved by processing the iron oxide in a continuous operation, namely:

(1) The necessity of cooling or quenching the black ferrosoferric oxide after heating is eliminated; there is no loss of batches of the oxide and fire hazard due to spontaneous combustion of the black oxide cannot occur be cause the black oxide never leaves the closed system;

'(2) Re-heating of the black ferrosoferric oxidepreviously cooledis unnecessary, because in our system the black oxide is processed when still hot from the foregoing reduction;

' (3) No special precautions are necessary, except to provide a careful dosage of the countercurrent air during the oxidation process; because the hot black ferrosoferric oxide, as it leaves the reduction zone, carries its own pro tection in theform of the reducing atmosphere. As the black oxide travels into the oxidation zone it gradually cools, loses the protecting reducing atmosphere which is in turn replaced by the countercurrent of oxidizing air. By that time the latter has already lost much of its oxygen, because it was absorbed earlier while passing over the partly oxidized material. The heat created by the exothermic oxidation reaction is therefore slowly released and cannot cause damage by overheating the product.

(4) Stability is imparted to the final product, at the end of the oxidation step, without damage to its magnetic properties. 7

(5) The total time in which the operation is performed is considerably reduced since our continuous process may be said to take about as much time as each of the two separate steps.

The apparatus employed for the purpose may take one-of several forms but the method is substantially the same.

The non-magnetic alpha ferric oxide is fed into an enclosed conveyor system at a predetermined rate of feed. The conveyor may be a flat belt passing through a vapor restricting heating section, or a slightly incl'med rotating tube, or a stationary tube with internal screw conveyor; or a round or flat vibratory conveyor. p a

In all cases, the conveyor may be considered asbeing divided into two operating zones, reducing and oxidizing. The first is a hot-reducing zone, heated in any suitable manner, such as electrically, by gas, or oil which is accurately controlled between 1000 F, and 1200" F. for optimum results. The second is a cooling-oxidizingzone which, for example, may be water-jacketed or water sprayed. If it is sufficiently long, it may be finned and air cooled. The two zones are advantageously of about the same length. Diameters, widths, heights, etc, maybe through-put required, fineness of particle size of the ferric oxide and degree of reduction-required.

Feeding of the raw material into the hot reducing zone should be regular and uniform and may be accomplished almost anything which has a high affinity for oxygen and cracks or decomposes at a reasonable temperature, that is, does not evaporate too quickly or fails to crack at the reaction temperature will work-for example, Wax, starch, kerosene, light fuel oil, ordinary low grade lubricating oil,

varnolene, etc- Actually we find almost any organic matterwith low ash and tar content which cracks below 1000 F. does well, and we use #3 fuel oil or cheap motor oil with great success. We prefer to mix-the oil directly into the alpha ferric oxide, in the proportions of about 3 to 5% by weight, depending of course on the reducing agent or agents employed, in order to have the active reducing gases permeate the oxide.

The heat of the reducing zone should be very uniform because underor over-heating even in small degree is deleterious to the magnetic properties of the iron oxide. Either very thin layers or good mixing of the material is indispensable to assure even heat treatment. With very fine powders, we find reduction takes place almost instantly. With larger particles or aggregates the required penetration time is substantially increased. Through-put rate and dwell or detention time are adjusted to give maximum yield with maximum magnetic properties.

At the intermediate portion between the heating and the cooling zones, we have a dampered tube which performs a dual function. First, it allows the escape of water vapor, spent gases and excess reducing gases; and, second, it acts to draw fresh air through the cooling zone in a counter flow direction.

The iron oxide at this mid point is deep black, magnetic and pyrophoric and at a temperature of about 1100 F. Obviously up to this time re-oxidation or ignition is impossible, because the material is in an oxygen-free reducing atmosphere. Even the temperature is far above that required for oxidation.

We now find that as the black ferrosoferric oxide passes into the cooling zone it meets with a small amount of oxygen depleted air. That is the air is very lean in oxygen and very rich in inert nitrogen. Oxidation begins immediately but at a gentle rate and the reaction is only slightly exothermic. As the iron oxide proceeds through the cooling zone the oxygen content of the atmosphere becomes progressively richer, the oxidation reaction more rapid, and the cooling action more positive.

By balancing the incoming fresh air from the gamma ferric oxide outlet end of the cooling zone, we allow the now almost cool iron oxide to meet completely fresh air; but, since the oxidizing reaction is almost complete, the danger of violent exothermic reaction is passed and the resulting gamma ferric oxide may be allowed to pass out of the kiln into fresh air without further precaution. The material may still be too hot to touch and of a dirty brown color but as soon as cooling is complete the oxide will assume a clean clear yellowish-brown color, of strong mag netic properties and completely stable.

We have built and operated three of these units, one of a rotating tube type, one of a fiat traveling belt type, and one of a stationary tube type with a screw conveyor inside. The last and latest seems to be the most satisfactory.

- These and other features of the invention will be better zone B. The stack is provided with a damper 42. The

understood by referring to the attached drawing, taken in conjunction with the following description, in which Fig. 1 is a longitudinal view, mostly in cross-section, of an apparatus illustrative of a practice of the invention;

Fig. 2 is a section on the line 22 of Fig. 1; and

Fig. 3 is a section on the line 33 of Fig. 1.

Referring to Fig. 1 and looking from right to left, the apparatus shown is divided generally into a feeding or charging zone A, a heating-reducing zone B, a gas venting zone C, a cooling-oxidizing zone D, a discharging zone E, and a power-driving zone F. As shown some, if not all, of the zones may overlap to some extent.

Feeding or charging zone A includes an inclined enclosed endless conveyor 10 with its discharge opening 11 extending over a funnel 12 with a fairly small outlet 13 communicating with the end portion of a generally horizontal conveyor tube 14 sealed at its end with a plate 15 provided with a shaft bearing 16. Outlet 13 is sufiiciently small to inhibit ingress of objectionable amounts of air with the alpha ferric oxide going into the conveyor tube for treatment.

As indicated above, various reducing agents may be employed. They may be gaseous, liquid, or solid, or a combination of two or more of them. In case a gaseous reducing agent is to be used, one preferably non-dangerous, it can be introduced through an inlet 20, having a valve 21, to the interior of the conveyor tube. In case a liquid reducing agent is to be used, it can be stored in a tank, from which depends a conduit 23, having a valve 24, over a funnel 25 connecting with a'conduit 26 communicating with the interior of the conveyor tube. The passageway of the conduit is sufficiently small in cross-section to remain filled with the liquid reducing agent and thus to keep outside air from seeping into the tube. in case a solid reducing agent is to be used, a similar arrangement may be employed. Liquid and solid reducing agents may of course be fed to the tube with theiron oxide.

Heating-reducing zone B includes electrical resistance means 34] wound spirally around the exterior of the conveyor tube, and connected to a source of electrical energy, not shown. That portion of the tube is provided with a thick covering of heat-insulating material 32, the same being surrounded by a metal casing 34 for protection and to help keep it in place.- A pyrometer 36 is secured to the top of the casing and makes thermal contact with the conveyor tube. In this way suitable temperature control inside the tube may be provided. 7

Some latitude is possible with the gas venting zone C. It is located advantageously intermediate the heating-reducing and the cooling-oxidizing zones. As shown it includes a stack 40 just rearwardly of the reducing-heating stack preferably communicates with the outside atmosphere so that excess reducing gases and other gaseous products of reduction may be vented to the outside where they will not annoy operators of the apparatus. Spaced a suitable distance from the stack is a combination inletoutlet tube 44 which may communicate with the inside atmosphere. It is provided with a damper 45. The stack may be said to rise from the far end portion-of the heating-reducing zone while the tube rises from or near the far end portion of the cooling-oxidizing zone.

Cooling-oxidizing Zone D includes water-cooling means 50, which advantageously is in the form of a waterjacket 52 around the conveyor tube with a water inlet 54 at one end and a water outlet 56 at the other end.

oxidizing air may be supplied to the cooling-oxidizing.

supplemental outside air may be driven into the tube,

as desired.

The far end of the conveyor tube terminates in an end plate 60 provided with a shaft bearing 62." The tube is fitted with a spiral conveyor 66 secured to a longitudinal shaft 68, one end of which fits in bearing 16 of end plate 15 and the other end of which fits in bearing 62 of end plate 60.

Power-driving zone F includes a motor 70, coupled with a speed reducer, having a drive shaft 72 coupled to shaft 66 in the conveyor tube.

The far or discharge end of the tube is provided with a depending outlet 80, so that treated iron oxide may be discharged into a removable container 82. That tube outlet may be employed also as an inlet for air, or some air, into the tube, For that reason the outlet is preferably no larger than that about necessary to discharge the treated iron oxide.

The screw conveyor is advantageously divided into two main parts structurally. The first part or half 86, which extends through the heating-reducing zone, as shown in Fig. 2, is of conventional design; that is, the spiral portion is continuously solid or imperforate from the shaft tothe ,tube. This helps to confine the iron oxide and the reducing agent between convolutions of the spiral, thereby assuring thorough mixing of the two when the reducing agent is non-volatilized as well as when it is volatilized. The reducingagent is thus made to mix with the iron oxide while it passes concurrently with the iron oxide toward the cooling-oxidizing zone. By the time the alpha ferric oxide passes through its treatment stage it is thoroughly heated and reduced toferrosoferric oxide.

- The secondrpart or half 88 of the screw conveyor, as shownin Fig. 3, is discontinuous or perforate. To this end the screw conveyor blade or rim 90 is mounted on a plurality. of relatively small spokes 92, 94, 6 equidistantly spaced spirally and 'circumferentiallyof the screw;. thus simulating a spider effect. causessome of the ferrosoferric oxide to advance through spaces 100, 102,104 inwardly of the spiral blade. The spiral blade as well as the spokes cause the ferrosoferiic oxide to become intimately intermixed or churned with air advancing countercurrently through the cooling conveyor tube.

The apparatus may beemployedas follows in a prac ticeof the invention. With the use of endless conveyor 10, a body of alpha ferric oxide 110 of suitable particle This structure tact ,withthe heated ferrosoferric oxide entering the coolhigher than atmospheric, thus preventing ingress of outside airdownwardly through the stack into the screw conveyor tube- Water 116 is passed through .inlet 54 into water jacket 52 and escapes through outlet 56 to cool the tube and its contents in the cooling-oxidizing zone. As indicated above, it is desirable'to have regulated amounts of air rise through outlet 80 into the far end of the tube, supplemental air being passed into the tube by means of fan 58 .through air-inlet 57. .It will thus be seen that as the highly heatedfer'rosoferric oxide leaves the heating-reducingzoneit ismet with a countercurrent of pre-. heated air in the cooling-oxidizing zone. As the. air advances through the conveyor tube, from left to right as one views Fig. 1 it gradually oxidizes the ferrosoferric oxide to form the desired gamma ferric oxide. Due to the. design of the screw conveyor in the cooling-oxidizing zone, the air is intimately admixed with the ferrosoferric oxide. As the air first enters the zone]: is relatively rich in oxygen; but the air becomes leaner in oxygen and relatively richer in inert nitrogen as it advances toward the heating-reducing zone; so that it is this oxygen-lean nitrogen-rich air that first comes into contact with the heated ferrosoferric oxide.

While, as indicated above, all of the air may be vented through stack 40, it is sometimes desirable to pass at least some of the air through tube 44 before it reaches stack 40. Damper 45 in tube 44 may be adjusted so that the air, water vapor and other gaseous oxidizing products are under positive pressure higher than atmospheric as they are vented, thus preventing ingress of air downwardly through the stack into the conveyor tube. Since tube 44 is spaced from stack 40, it reduces the opportunity for even the oxygen-lean air to come in coning-oxidizing zone. On the other hand, it may be desirableisometimes to let some air pass downwardly through tube 44 toconveyor tube14 to supplement that coming from air-inlet 57.

By the time the ferrosoferric oxide advances through the entire length of the cooling-oxidizing zone it is sub stantially completely converted to the highly desired gamma ferric oxide. This oxide drops by gravity through outlet 80 into container 82 without any danger of catchsize, is loaded at. a predetermined rate into funnel 12,

from .which it drops by gravity gradually through outlet 13 into the. interior of screw conveyor tube 14. Motor is .set intooperation, the rotation of its drive shaft 72 being inadirection to cause the ferric oxide to advance inthe. tube. from right to left, as one views Fig. l. Due-tothe constricted size of outlet 13, substantially no outside air is admitted to the tube, thus preventing the creationof oxidizing conditions inthe heating-reducing zone by virtue of such air. The tubegradually fills up to-its normal work level throughout its entire length. Heating means. 30. are employed toheat the ferric oxide indirectly, the -amountof .heat supplied being regulated. in accordance with the temperature indications of pyrometer 36.

- As already indicated, each spiral convolution .of the spiral conveyor in. the heating-reducing zonetends to retain its body of theferric. oxide in contact with the reducing agent.

Due tothe increase in temperature the reducing agent is cracked or decomposed gradually and is intimately intermixed with the alpha ferric oxide particles. The net result is -to subject the oxide particles to reductionas they advance through the heating-reducing zone/co form ferrosoferric oxide.

As the spentand unspent gaseous reducing agent and other gaseous products resulting from the reduction operation reach the entrance tostack 40, they risetherethrough andesca'pe tothe outside atmosphere. .Damper42 may be regulated so-that-theexiting gases are under pressure blackferrosoferricoxide. This is done by closing all The present apparatus includes a 20- foot thin wall steel tube about 10 inches in diameter with a 1 inch iron oxide inlet and a 2 inch iron oxide outlet. The hot zone,

about 9' feet long, is electrically heated and requires- The vapor exhaust stack is a 2 inch pipe with butterfly valve and is located just after the hot zone and is approximately in the top of the middle of the tube. Water cooling is supplied only on the last half of the coolingoxidizing zone; An extra air inlet is provided just before min the water-cooling zone;and a small fan with damper may supply extra air under slight pressure, if the reducing gases tend to encroach on the cooling-oxidizing zone and are not completely carried away by the exhaust stack The .reducingmaterials'we prefer are light fuel oil or low grade engine oil which We mix in with the alpha ferric oxide at the time of screening before feeding to the conveyor tube. However, oil may be dripped onto the ironoxide in the feed funnel.

In actual practice the converter is started by making the'dampers. Temperature is adjusted to give optimum magnetic, properties. Feed. and speed are adjusted to give uniform conversion and maximum through-put.

When ,thcse'constamsare sta li h We h 12 air stack dampers and if necessary start the small fan. Within about ten minutes the black oxide turns from black to. brown; if too dark we increase the air; ifreddish, the forced draft is decreased. Visaul color is the only necessary guide at this point. A light clear yellow brown indicates that oxidation is complete. Redness. or red particles or particles containing red cores indicate the material has burned and is now admixed with non-magnetic alpha ferric oxide. j r

This unit manufactures gamma ferric oxide at the minimum rate of about 50 lbs. an hour and a maximum of about 70 lbs. 1

It will be clear to those skilled in the art that the above is by way of example,.and that the practice of the invention readily lends itself to a number of useful modie fications. p.

Reference may be .made to our copending application Serial No. 526,269 filed simultaneously with the present application for claims directed to the methodvherein disclosed.

We claim:

1. In apparatus for converting non-magnetic alpha ferric oxide into magnetic gamma ferric oxide suitable for magnetic impulse record members and the like, the improvement comprising an elongated chamber divided generally into a heating-reducing zone and a coolingoxidizing zone, the two zones being in open communication with each other, means for heating the heatingreducing Zone, means for cooling the cooling-oxidizing zone, an inlet in the charging end of the heating-reducing zone for feeding non-magnetic alpha ferric oxide thereto, an inlet in the charging end of the heating-reducing zone for-the introduction of a reducing agent, means for progressively advancing a body of ferric oxide continuously and successively through the two zones, an outlet for the vwithdrawal of spent gases from theiheating reducing zone and the cooling-oxidizing zone positioned intermediate the length of the chamber and extending from the chamber adjacent the location where'the heating-reducing zone terminates and the cooling-oxidizing zone begins, an inlet in the discharging end of the coolingoxidizing zone for the introduction of air, an outlet in the discharging end of the cooling-oxidizing zonefor the withdrawal of magnetic gamma ferric oxide, means for causing the reducing agent to pass through the heating-1 reducing zone concurrently with the movement of the ferric oxide therethrough, and means for causing the air to flow through the cooling-oxidizing zone countercurrently to the movement of the ferric oxide therethrough.

2. Apparatus according to claim 1, in which the air inlet in the discharging end of the cooling-oxidizing zone 1s provided with means for forcing a draft of the air'into and through said zone.

3. Apparatus according to claim 1, in which the air inlet and the ferric oxide outlet in the discharging end of the cooling-oxidizing zone are spaced from one another.

4. Apparatus according to claim 1, in which a second outlet for spent oxidizing air is provided at the charging end of the cooling-oxidizing zone for the withdrawal'of spent oxidizing 'air from said' zone, said outlet being spaced from said gas withdrawal outlet which extends from the location where the heating-reducing zone terminates and the cooling-oxidizing zone begins to inhibit passage of oxidizing gas from the cooling-oxidizing zone into the heating-reducingzone. g V

5. Apparatus according to claim 1, in which the chamber is in the form of an'elongated tube, and thetube is fitted with a power-driven screw conveyor to advance the iron oxide therethrough.

6. Apparatus according to claim 1, in which the chamber is in the form of an elongated tube, the tube is fitted with apoWer-driven screw conveyor to advance the ferric oxide therethrough, andthe screw conveyor is perforate its cross-sectional area in the cooling-oxidizing zone so that the oxidizing .agent may be freely intermixed the iron oxide while it is in transit.

7. Apparatus according to claim inlet in the discharging end of the cooling-oxidizing zone is provided with means for forcing a draft of the air into and through the zone, andtthe air inlet and ferric oxide outlet in the discharging end, of the cooling-oxidizing zone are spaced from one another. w a p 8. Apparatus according to claim 1, in which the air inlet in the discharging end of the cooling-oxidizing zone is provided with means for forcing a draft of the air into and through the zone, and an outlet is provided at thecharging end of the cooling-oxidizing zone for. the With-- drawal of spent oxidizing air from the chamber.

9. Apparatus according to claim 1, in which the air inlet in the discharging end of the cooling-oxidizing zone is provided with means for forcing a draft of the air into and through the zone, an outlet is provided at the charg ing end of the cooling-oxidizing zone for the withdrawal of spent oxidizing air from the chamber, and the latter outlet is spaced from said gas withdrawal outlet which extends from the location where the heating-reducing zone terminates and the cooling-oxidizing zone begins toinhibit passage of oxidizing gas from the cooling-oxidizing zone into the heating-reducing zone. 7

10. Apparatus according to claim 1, in which the chamber is in the form of an elongated tube, the tube is fitted with a power-driven screw conveyor to advance the ferric oxide therethrough, and the screw conveyor isimperforate in the heating-reducing zone so that the reduc ing agent may be freely intermixed with the iron oxide between convolutions of the screw conveyor while the iron oxide is in transit. v

11. Apparatus according to claim 1, in which the chamber is in the form of an elongated tube, the tube is fitted with a power-driven screw conveyor to advance the ferric oxide therethrough, the screw conveyor is perforate in its cross sectional area in the cooling-oxidizing zone so that the oxidizing agent may be freely intermixed with the iron oxide while it is in transit, and the screw conveyor is imperforate in its cross sectional area in the heating-reducing zone so that the reducing agent may be freely intermixed with the iron oxide between convolutions of the screw conveyor while the iron oxide is in transit. v

12. In apparatus for converting'non-magnetic alpha. ferric oxide into magnetic gamma ferric oxide suitable for magnetic impulse record members and the like, the improvement comprising an elongated chamber. divided generally into a heating-reducing zone and a cooling:

oxidizing zone, the two zones being in open communication with each other, means for heating the. heating: reducing zone, means for cooling the cooling-oxidizing zone, an inlet in the charging end of the heatirigreducing zone for feeding non-magnetic alpha ferric oxide thereto, an inlet in the charging end of the heating-reducingzone for the introduction of a reducing agent, means for pro gressively advancing a body of ferric oxide continuously and successively through the two zones, an outlet passag -I way for the withdrawal of spent gases from the heating: reducing zone and the cooling-oxidizing zone intermediate the length of the chamber and extending from the chamber adjacent the location where the heating-reducing-zone terminates and the cooling-oxidizing zone begins, the, inner end of the outlet passageway terminating at the topmost part of the chamber, an inlet in the discharging end of the cooling-oxidizing zone for the introduction of air, and an outlet in the discharging end of thecooling oxidizing zone for the withdrawal of magnetic ferric oxide.

1, in which theair 

1. IN APPARATUS FOR CONVERTING NON-MAGNETIC ALPHA FERRIC OXIDE INTO MAGNETIC GAMMA FERRIC OXIDE SUITABLE FOR MAGNETIC IMPULSE RECORD MEMBERS AND THE LIKE, THE IMPROVEMENT COMPRISING AN ELONGATED CHAMBER DIVIDED GENERALLY INTO A HEATING-REDUCING ZONE AND A COOLINGOXIDIZING ZONE, THE TWO ZONES BEING IN OPEN COMMUNICATION WITH EACH OTHER, MEANS FOR HEATNG THE HEATINGREDUCING ZONEM MEANS FOR COOLING THE COOLING-OXIDIZING ZONE, AN INLET IN THE CHARGING END OF THE HEATING-REDUCING ZONE FOR FEEEING NON-MAGNETIC ALPHA FERRIC OXIDE THERETO, AN INLET IN THE CHARGING END OF THE HEATING-REDUCING ZONE FOR THE INTRODUCTION OF A REDUCING AGENT, MEANS FOR PROGRESSIVELY ADVANCING A BODY OF FERRIC OXIDE CONTINUOUSLY AND SUCCESSIVELY THROUGH THE TWO ZONES, AN OUTLET FOR THE WITHDRAWAL OF SPENT GASES FROM THE HEATINGREDUCING ZONE AND THE COOLING-OXIDIZING ZONE POSITIONED INTERMEDIATE THE LENGTH OF THE CHAMBER AN EXTENDING FROM THE CHAMBER ADJACENT THE LOCATION WHERE THE HEATING-REDUCING ZONE TERMINATES AND THE COOLING-OXIDIZING ZONE BEGINS, AN INLET IN THE DISCHARGING END OF THE COOLINGOXIDIZING ZONE FOR THE INTRODUCTION OF AIR, AN OUTLET IN THE DISCHARGING END OF THE COOLING-OXIDIZING ZONE FOR THE WITHDRAWAL OF MAGNETIC GAMMA FERRIC OXIDE, MEANS FOR CAUSING THE REDUCING AGENT TO PASS THROUGH THE HEATINGREDUCING ZONE CONCURRENTLY WITH THE MOVEMENT OF THE FERRIC OXIDE THERETHROUGH, AND MEAND FOR CAUSING THE AIR TO FLOW THROUGH THE COOLING-OXIDIZING ZONE COUNTERCURRENTLY TO THE MOVEMENT OF THE FERRIC OXIDE THERETHROUGH. 